Field of the Invention
The present invention relates to display devices, and in particular to display devices using thin film transistors (TFTs).
Description of the Related Art
In order to fulfill the requirements of high-speed image processing and high-quality image displays, flat-panel displays, such as color liquid-crystal displays (LCDs) have become popular. LCDs typically have an upper and a lower substrate with electrodes thereon. These substrates are sealed with adhesive materials, and a liquid-crystal material is sealed between these two substrates. Prior to liquid-crystal injection, spacers are sprayed between the substrates in order to maintain a constant distance therebetween.
Thin film transistors (TFTs) are typically formed above the lower substrate as switching devices. Each TFT has a gate electrode connected to a scanning line, a source electrode connected with a data line, and a drain electrode connected to a pixel electrode. The upper substrate is disposed above the lower substrate and includes a color filter and a plurality of light-shielding materials (formed of resin black matrix, for example). Edges of the lower and upper substrates are sealed with adhesive materials, and liquid-crystal materials are provided between the upper and lower substrates. The lower substrate is also called a first substrate, and elements such as TFTs and electrical contacts are formed thereover, which are typically defined by performing several photolithography steps.
However, as improvements are made in the image resolution of display devices, display devices for maintaining or improving the performance of the aperture ratio and image display of display devices are needed, especially as the size of the elements such as TFTs and contacts formed over the lower substrate is further reduced.